1. Introduction
Willow, belonging to Salicaceae family contains notable amount of bioactive compounds
[18] | Nora Tawfeek, Mona F. Mahmoud, Dalia I Hamdan, Mansour Sobeh, Nawaal Farrag, Michael Wink, Assem M. EI-Shazly. Phytochemistry, Pharmacology and Medicinal Uses of Plants of the Genus Salix: An Updated Review. Front Pharm. 2021; 12: 593856: 1-30. https://doi.org/10.3389/fphar.2021.593856 |
[18]
. Especially, willow bark, known to have anti-inflammatory and anti-nociceptive functions has been used as traditional medicine since ancient times
[15] | Le N. P. K., Herz C., Gomes J. V. D., Förster N., Antoniadou K., Mittermeier-Kleßinger V. K., Mewis I., Dawid C., Ulrichs C., Lamy E. Comparative Anti-Inflammatory Effects of Salix Cortex Extracts and Acetylsalicylic Acid in SARS-CoV-2 Peptide and LPS-Activated Human In Vitro Systems. Int J Mol Sci. 2021; 22: 6766. https://doi.org/10.3390/ijms22136766 |
[20] | Reshamwala D, Shro S, Liimatainen J, Tienaho J, Laajala M, Kilpeläinen P, Viherä-Aarnio A, Karonen M, Jyske T, Marjomäki V. Willow (Salix spp.) bark hot water extracts inhibit both enveloped and non-enveloped viruses: study on its anti-coronavirus and anti-enterovirus activities. Front Microbiol. 2023; 14: 1249794. https://doi.org/10.3389/fmicb.2023.1249794 |
[15, 20]
. It was regarded that pharmaceutical activity of willow bark was attributed to salicylate compounds after the discovery of aspirin. However, pharmacological studies have indicated that not only salicylate derivatives but also other active components of willow bark (e.g. polyphenols, flavonoids) play an important role in the analgesic and anti-inflammatory activity
. Willow bark extracts contain different kinds of phenolic compounds such as gallic acid, caffeic acid, canillin, catechin, epigallocatechin gallate, rutin, quercetin and so on
[5] | Bernd Kammerer, Rainer Kahlich, Claudia Biegert, Christoph H. Gleiter, Lutz Heide. HPLC-MS/MS Analysis of Willow Bark Extracts Contained in Pharmaceutical Preparations. Phytochem Anal. 2005; 16: 470-478. https://doi.org/10.1002.pca.873 |
[5]
. Therefore, willow bark extract may have different mechanism from aspirin
[22] | Vlachojannis J., Magora F., Chrubasik S. Willow Species and Aspirin: Different Mechanism of Actions. Phytothera Res. 2011; 25: 1102-1104. https://doi.org/10.1002/ptr.3386 |
[22]
.
Although bioactive compounds in willow bark extract exhibit various physiological activities, they have some drawbacks in clinic application. For example, saligenin, hydrolysis form of salicin in the stomach, is known to damage the gastrointestinal mucosa
[3] | Akao T, Yoshino T, Kobashi K, Hattori M. Evaluation of salicin as an antipyretic prodrug that does not cause gastric injury. Planta Med. 2002; 68: 714-718. https://doi.org/10.1055/s-2002-33792 |
[3]
. In addition, phenolic compounds in extract generally have low bioavailability and stability, which hinders their clinic application
[16] | Liu C. Z., Ge S. J., Yang J., Xu Y. Y., Zhao M., Xiong L., Sun Q. J. Adsorption mechanism of polyphenols onto starch nanoparticles and enhanced antioxidant activity under adverse conditions. J Funct Foods. 2016; 26: 632–644. |
[16]
. Willow bark extract is also difficult to handle because it is in liquid form.
The encapsulation approach could provide a perfect solution to these problems. Encapsulation has been studied for many years in food and medicine industry. It enables to improve bioavailability and stability of bioactive materials, to modify sensory properties of stimulant ingredients and to control release of drug
[9] | Diego F. Montoya‑Yepes, Angel A. Jiménez‑Rodríguez, Alvaro E. Aldana‑Porras, Luisa F. Velásquez‑Holguin, Jonh J. Méndez‑Arteaga, Walter Murillo‑Arango. Starches in the encapsulation of plant active ingredients: state of the art and research trends. Polym Bulletin. 2023; 1-29. |
[9]
. In encapsulation process, selection of wall material is important. Wall materials in pharmaceutical and food industry should be GRAS (Generally Regarded As Safe), therefore natural polymers such as starch, Arabic gum, maltodextrin, pectin, cellulose and protein are currently available due to their non-toxicity, bioavailability and low cost. Among them, starch has gained a growing interest of scientists due to its advantages such as biocompatibility, low cost and hypoallergenic character
[9] | Diego F. Montoya‑Yepes, Angel A. Jiménez‑Rodríguez, Alvaro E. Aldana‑Porras, Luisa F. Velásquez‑Holguin, Jonh J. Méndez‑Arteaga, Walter Murillo‑Arango. Starches in the encapsulation of plant active ingredients: state of the art and research trends. Polym Bulletin. 2023; 1-29. |
[10] | Gislaine F. N., Luiz G. P. M., Farayde M., Fakhouri, Rafael, Augustus de Oliveira. Microencapsulation of blackberry pulp with arrowroot starch and gum arabic mixture by spray drying. J. Microencapsul. 2018 (in press). https://doi.org/10.1080/02652048.2018.1538264 |
[9, 10]
. Previous studies on starch as a coating material have proved that starch has good characteristics such as high encapsulation efficiency, oxidation stability, releasing parameters and cellular absorption. Over the last decade, the research of using starch as a wall material has focused on multiple starch source and its modified forms to encapsulate active materials at micro- and nanoscale with and without other polymers
[7] | Daniela Borrmann, Anna Paola Trindade Rocha Pierucci, Selma Gomes Ferreira Leite, Maria Helena Miguez da Rocha Leão. Microencapsulation of passion fruit (Passiflora) juice with n-octenylsuccinate-derivatised starch using spray-drying. Food Bioprod Process. 2013; 91: 23–27. https://doi.org/10.1016/j.fbp.2012.08.001 |
[8] | Diego F. Montoya Yepes, Walter Murillo Arango, Angel Arturo Jim ´ ´enez Rodríguez, Jonh Jairo M´endez Arteaga, Alvaro Esteban Aldana Porras. Encapsulation of phenols of gulupa seed extract using acylated rice starch: Effect on the release and antioxidant activity. J Funct Foods. 2021; 87: 104788. https://doi.org/10.1016/j.jff.2021.104788 |
[9] | Diego F. Montoya‑Yepes, Angel A. Jiménez‑Rodríguez, Alvaro E. Aldana‑Porras, Luisa F. Velásquez‑Holguin, Jonh J. Méndez‑Arteaga, Walter Murillo‑Arango. Starches in the encapsulation of plant active ingredients: state of the art and research trends. Polym Bulletin. 2023; 1-29. |
[10] | Gislaine F. N., Luiz G. P. M., Farayde M., Fakhouri, Rafael, Augustus de Oliveira. Microencapsulation of blackberry pulp with arrowroot starch and gum arabic mixture by spray drying. J. Microencapsul. 2018 (in press). https://doi.org/10.1080/02652048.2018.1538264 |
[11] | Graciele L. N., Brunna C. B. B., Stephanie S. P., Silvani V., Fábio S. M., Elane S. P., Renata D. M. C. A. Microencapsulation of freeze concentrated Ilex paraguariensis extract by spray drying. J Food Eng. 2015; 151: 60-68. https://doi.org/10.1016/j.jfoodeng.2014.10.031 |
[7-11]
.
Starches with type B crystallinity, such as potato starch could trap and protect bioactive molecules
[9] | Diego F. Montoya‑Yepes, Angel A. Jiménez‑Rodríguez, Alvaro E. Aldana‑Porras, Luisa F. Velásquez‑Holguin, Jonh J. Méndez‑Arteaga, Walter Murillo‑Arango. Starches in the encapsulation of plant active ingredients: state of the art and research trends. Polym Bulletin. 2023; 1-29. |
[9]
. Researches proved that potato starch could produce more homogenous particles for encapsulating of phenolic compounds compared to maltodextrins
[1] | Adejoro F, Hassen A, Thantsha M. Characterization of starch and gum arabic-maltodextrin microparticles encapsulating acacia tannin extract and evaluation of their potential use in ruminant nutrition. Asian-Australas J Anim Sci. 2019; 32: 977–987. |
[1]
.
Spray drying is the most used encapsulation technique due to its efficiency, continuous production and ease of industrialization. It is a technological process in which liquid product is changed into a powder in a single processing step
[9] | Diego F. Montoya‑Yepes, Angel A. Jiménez‑Rodríguez, Alvaro E. Aldana‑Porras, Luisa F. Velásquez‑Holguin, Jonh J. Méndez‑Arteaga, Walter Murillo‑Arango. Starches in the encapsulation of plant active ingredients: state of the art and research trends. Polym Bulletin. 2023; 1-29. |
[9]
. Spray dryers utilize atomizer or spray nozzle to disperse the liquid. Water evaporation occurs when spray and drying medium contact. This technology is well established and straightforward.
In our preliminary experiment, we obtained yellow powder from willow bark extract by spray drying. However, this powder has some intrinsic drawbacks such as stickiness, hygroscopicity and astringency. Therefore, high molecular weight encapsulating agents such as starch should be used together to solve such problems.
There have been attempts to encapsulate bioactive molecules using starch as a wall material. For example, yerba mate extracts, gulupa seed extracts, polyphenols from olive pomace, black berry extract, green tea bioactive compounds were successfully encapsulated by starch
[8] | Diego F. Montoya Yepes, Walter Murillo Arango, Angel Arturo Jim ´ ´enez Rodríguez, Jonh Jairo M´endez Arteaga, Alvaro Esteban Aldana Porras. Encapsulation of phenols of gulupa seed extract using acylated rice starch: Effect on the release and antioxidant activity. J Funct Foods. 2021; 87: 104788. https://doi.org/10.1016/j.jff.2021.104788 |
[10] | Gislaine F. N., Luiz G. P. M., Farayde M., Fakhouri, Rafael, Augustus de Oliveira. Microencapsulation of blackberry pulp with arrowroot starch and gum arabic mixture by spray drying. J. Microencapsul. 2018 (in press). https://doi.org/10.1080/02652048.2018.1538264 |
[11] | Graciele L. N., Brunna C. B. B., Stephanie S. P., Silvani V., Fábio S. M., Elane S. P., Renata D. M. C. A. Microencapsulation of freeze concentrated Ilex paraguariensis extract by spray drying. J Food Eng. 2015; 151: 60-68. https://doi.org/10.1016/j.jfoodeng.2014.10.031 |
[17] | Marco Paini, Bahar Aliakbarian, Alessandro A. Casazza, Alberto Lagazzo, Rodolfo Botter, Patrizia Perego. Microencapsulation of phenolic compounds from olive pomace using spray drying: A study of operative parameters. LWT - Food Sci Technol. 2015; 1-10. https://doi.org/10.1016/j.lwt.2015.01.022 |
[21] | Teixeira A. S., Navarro A. S., Molina-Garcia A. D., Martino M., Deladino L. Corn starch systems as carriers for yerba mate (Ilex paraguariensis) antioxidants: Effect of mineral addition. Food Bioprod Process. 2015; 94; 39–49. https://doi.org/10.1016/j.fbp.2015.01.002 |
[23] | Zhang L. M., Hu Z. Y., Yan L. H., Li R. L., Cao C. W., Hu X. D. Preparation and Characterization of Tea Polyphenols/Starch Inclusion Complex. Appl Mech Mater. 2013; 432: 413-417. https://doi.org/10.4028/www.scientific.net/AMM.432.413 |
[8, 10, 11, 17, 21, 23]
. However, to our knowledge, this is the first report to encapsulate willow bark extract by spray drying. The present study aimed to obtain powder from willow bark extract with starch by spray drying and characterize encapsulated material.
2. Materials and Methods
2.1. Materials
2.1.1. Chemicals
Folin-Ciocalteu phenol reagent, salicin and gallic acid were purchased from Sigma Chemical Co. (USA). Native potato starch (amylose content 20-25%) was purchased from Samjiyon Potato Flour Production Factory (DPRK). All other reagents were of analytical grade.
2.1.2. Plant Material and Preparation of Willow Bark Extract
For the willow bark extraction, 2-year-old shoots of the willow trees (S. Koraiensis Anderson) growing around the riverside of Taedong in Pyongyang were harvested in April 2023. The shoots were cut to 30-cm-long pieces and immediately debarked. The obtained willow bark was dried in an air circulation oven (101-1AE, China) at 40°C until constant weight and ground in a mill. The samples were packed in plastic bags and stored at 4°C until preparation of willow bark extract.
Willow bark extract was prepared according to the methodology with some modification
[20] | Reshamwala D, Shro S, Liimatainen J, Tienaho J, Laajala M, Kilpeläinen P, Viherä-Aarnio A, Karonen M, Jyske T, Marjomäki V. Willow (Salix spp.) bark hot water extracts inhibit both enveloped and non-enveloped viruses: study on its anti-coronavirus and anti-enterovirus activities. Front Microbiol. 2023; 14: 1249794. https://doi.org/10.3389/fmicb.2023.1249794 |
[20]
. Briefly, ten kilogram of dry willow bark was added into a 100 L extraction system and filled with deionized water. The extraction temperature was 90°C and the extraction time was 60 min. Finally, the extract was filtered and stored at 4°C before experiment. Dry matter content of the prepared willow bark extract amounted to 3.5 wt%.
2.2. Methods
2.2.1. Encapsulation of Willow Bark Extract by Spray Drying
Potato starch (20 g) was suspended in 300 mL of distilled water. The mixture was gelatinized at 80°C for 20 min with continuous stirring. Then, 600 mL of willow bark extract was dropped to the mixture under the constant stirring. The solution obtained was sprayed by a spray dryer (LPG-5, China). The inlet and outlet temperatures were 150°C and 80°C, respectively. Compression air pressure and feed velocity were 0.4 MPa and 2 L/h, respectively.
On the other hand, the same amount of willow bark extract used for encapsulation was sprayed without starch addition to obtain willow bark extract powder. This free extract powder was used for control.
2.2.2. Characterization of the Encapsulated Powder
1) Salicin & total polyphenol content and encapsulation efficiency.
Encapsulation Efficiency (EE%) was measured according to the method
[7] | Daniela Borrmann, Anna Paola Trindade Rocha Pierucci, Selma Gomes Ferreira Leite, Maria Helena Miguez da Rocha Leão. Microencapsulation of passion fruit (Passiflora) juice with n-octenylsuccinate-derivatised starch using spray-drying. Food Bioprod Process. 2013; 91: 23–27. https://doi.org/10.1016/j.fbp.2012.08.001 |
[7]
. Briefly, a certain amount of encapsulates was dissolved in water. This water suspension was centrifuged at 12 000 rpm for 10 min. The supernatant solution was collected and filtered with a 0.45 µm FH membrane (Millipore, USA). Salicin content in supernatant (salicin residual) was quantified by HPLC (Shimadzu, Japan) according to the previous report
[5] | Bernd Kammerer, Rainer Kahlich, Claudia Biegert, Christoph H. Gleiter, Lutz Heide. HPLC-MS/MS Analysis of Willow Bark Extracts Contained in Pharmaceutical Preparations. Phytochem Anal. 2005; 16: 470-478. https://doi.org/10.1002.pca.873 |
[5]
. Total polyphenol content in supernatant (polyphenol residual) was evaluated by Folin-Ciocalteu
[8] | Diego F. Montoya Yepes, Walter Murillo Arango, Angel Arturo Jim ´ ´enez Rodríguez, Jonh Jairo M´endez Arteaga, Alvaro Esteban Aldana Porras. Encapsulation of phenols of gulupa seed extract using acylated rice starch: Effect on the release and antioxidant activity. J Funct Foods. 2021; 87: 104788. https://doi.org/10.1016/j.jff.2021.104788 |
[8]
. Total polyphenol was expressed as milligrams of gallic acid equivalents (GAE) per gram of dried powder.
The Encapsulation Efficiency was calculated by using the following equation:
EE (%) ofsalicin= (salicincontent initial-salicinresidual)/ (salicininitial) ×100
EE (%) of total polyphenols = (Phenolic compounds initial-Phenolic compounds residual)/ (Phenolic compounds initial) ×100
2) Moisture content. The moisture content of the encapsulated powder was determined according to the method described by
[11] | Graciele L. N., Brunna C. B. B., Stephanie S. P., Silvani V., Fábio S. M., Elane S. P., Renata D. M. C. A. Microencapsulation of freeze concentrated Ilex paraguariensis extract by spray drying. J Food Eng. 2015; 151: 60-68. https://doi.org/10.1016/j.jfoodeng.2014.10.031 |
[11]
. Samples were placed in an oven at 105 ºC until reaching constant weight.
3) Morphology and particle size. Morphological feature and particle size of the spray dried powder were characterized by a Jeol scanning electron microscopy model JSM-6610A (SEM, JEOL, USA) at an accelerating voltage of 10 kV. The samples were coated with gold and examined at 200×, 500×, 1600× magnifications. Approximately 100 particles from different powders were measured to calculate their average diameter.
4) Zeta-potential. Zeta potential of encapsulated particles was determined to characterize particle suspension by zeta potential analyzer (Malvern, UK).
5) Fourier transform infrared (FTIR) spectroscopic analysis. FTIR experiments were performed to identify the functional groups present in native starch, willow bark extract and encapsulated particles. This experiment was carried out using Fourier Transform Infrared Spectrometer (Nicolet, USA) in the range of 400-4000 cm-1.
6) X-ray diffraction (XRD). Willow bark extract, native starch and encapsulated powder were analyzed by an X-ray diffractometer (Siemens D5000, Germany) using a Cukα radiation source (40 KV, 40 mA). The scan range was 5º-70º and the speed was 0.5 degrees with 2 θ/min.
7) Thermal stability and degradation behaviors. The thermal stability and degradation behaviors were investigated by thermogravimetry/derivative thermogravimetry analysis. Each graph was obtained from a TGA 50-H (Shimadzu TGA 50-H, Japan). Approximately 7 mg of encapsulated powder, starch and willow bark extract were placed in aluminum pans and heated from 20°C to 900°C at a rate of 20°C /min.
8) Hygroscopicity. Hygroscopicity was measured according to previous methodology with some modification
[10] | Gislaine F. N., Luiz G. P. M., Farayde M., Fakhouri, Rafael, Augustus de Oliveira. Microencapsulation of blackberry pulp with arrowroot starch and gum arabic mixture by spray drying. J. Microencapsul. 2018 (in press). https://doi.org/10.1080/02652048.2018.1538264 |
[10]
. Ten gram of encapsulated and free extract powder was placed in a container at 25ºC with a saturated NaCl solution, corresponding to a 75.3% relative humidity environment. The samples were weighed after 3 days. The hygroscopicity was measured in gram of adsorbed water per 100 g of dry solid.
9) Storage stability. Storage stability of the encapsulated powder and the control (free willow bark extract) were tested according to previous method
[11] | Graciele L. N., Brunna C. B. B., Stephanie S. P., Silvani V., Fábio S. M., Elane S. P., Renata D. M. C. A. Microencapsulation of freeze concentrated Ilex paraguariensis extract by spray drying. J Food Eng. 2015; 151: 60-68. https://doi.org/10.1016/j.jfoodeng.2014.10.031 |
[11]
. Briefly, an amount of 10 g of encapsulated powder and willow bark extract powder were placed in closed petri dishes and stored in the dark at 4 ºC for 50 days. Every 10 days, samples were taken and measured the total polyphenol content by Folin-Ciocalteu method.
10) Statistical analysis. Each assay was performed in triplicate (n=3). Results were expressed as the mean ±standard deviation (SD). Analysis of variance (ANOVA) was used to evaluate the comparison of formulations.
3. Result and Discussion
3.1. Salicin, Total Polyphenol Contents and Encapsulated Efficiency
Spray drying is a powerful technology to encapsulate bioactive molecules. However, the main disadvantage of spray drying is the use of high temperature, which is not suitable for heat sensitive ingredients. On the other hand, if the temperature is too low, the produced powder may exhibit high moisture content. In previous literature, the author used a low temperature of 130ºC for preserving nutraceutical features of green tea extract
[4] | Ana B. C., Steva L., Ana K., Igor Š., Verica Đ., Draženka K., Gordan M., Viktor N. Efficiency Assessment of Natural Biopolymers as Encapsulants of Green Tea (Camellia sinensis L.) Bioactive Compounds by Spray Drying. Food Bioprocess Technol. 2015: 1-17. https://doi.org/10.1007/s11947-015-1592-y |
[4]
. Therefore, taking into account the heat stability of salicin (around 190°C) and polyphenols in willow bark extract, the inlet temperature was set to 150°C. After spray drying, the moisture content of the powder obtained was below 5% (3.7±0.3%), which implies good stability. The encapsulation efficiency was 75.71±0.02% (polyphenols) and 57.8±0.25% (salicin), respectively.
3.2. Particle Size and Morphology of Encapsulated Powder
Particle size plays an important role in the stability of the systems. The particle size and distribution are closely related to the releasing behavior. The SEM result indicated that spray dried powder had micro level size with the average diameter of 17.9 µm, ranging from 8.2 to 27 µm.
The shape and morphology of the encapsulated particles were shown in
Figure 1. As can be seen in
Figure 1, the encapsulated particles had a regular, spherical shape with extensive dented surface. Formation of dented surfaces was presumed due to the shrinkage of the particles during the drying process
[13] | Jarunee Loksuwan. Characteristics of microencapsulated β-carotene formed by spray drying with modified tapioca starch, native tapioca starch and maltodextrin. Food Hydrocoll. 2007; 21: 928-935. https://doi.org/10.1016/j.foodhyd.2006.10.011 |
[13]
.
Figure 1. Scanning Electronic Microscopy of encapsulated powder. (A) 200×(B) 500× (C) 1600× Magnification.
3.3. Zeta-Potential
Zeta-potential is an important parameter to evaluate suspension of particles. High zeta potential values mean electrostatic repulsion, which is ideal for the stability. Zeta-potential of encapsulated particle was -18.5 mV (
Figure 2), similar to -20.1 mV published in previous result where catechin was encapsulated by using starch
[2] | Ahmad M, Mudgil P, Gani A, Hamed F, Masoodi F, Maqsood S. Nano-encapsulation of catechin in starch nanoparticles: characterization, release behavior and bioactivity retention during simulated in-vitro digestion. Food Chem. 2019; 270: 95–104. |
[2]
.
If the zeta potential of a solution is between -18 mV and +18 mV, this solution may be instable and inappropriate for intravenous administration. However, because our goal was to develop willow bark extract carrier for oral administration, we assumed that it does not cause any serious problem. Negative charge of the particle may be attributed to the particles with loading negative charged polyphenols.
Figure 2. Zeta-potential of encapsulated particles.
3.4. FTIR
Figure 3 depicts the FTIR spectra of native starch, willow bark extract and encapsulated particles. As shown in
Figure 3, the FTIR spectra of native starch and encapsulated particles showed similar intensity bands with slight differences in some peaks. The broad absorption peak around 3400 cm
-1 was attributed to hydroxyl group and its inter and intramolecular interaction. Compared to starch and willow bark extract, in encapsulated particle, a shift towards lower frequency (3403 cm
-1) was observed, suggesting the formation of intermolecular hydrogen bonds.
Figure 3. FTIR spectra of starch, willow bark extract and encapsulated powder.
The other characteristic bands at around 2900 cm
-1 were assigned to –CH
2 stretching vibrational modes and that at around 1640 cm
-1 was attributed to bound water. Willow bark extract showed several characteristic bands: the broad band around 3400 due to O-H stretching of hydroxyl groups; a band around 1620, 1450, 1270 and 1070 due to the stretching of aromatic rings. Notably, willow bark extract and encapsulated extract showed almost identical characteristic spectrum, especially from 800-1500 cm
-1 (fingerprint region), indicating that integrity of willow bark extract was preserved after spray drying and bioactive molecules were incorporated in the starch
[4] | Ana B. C., Steva L., Ana K., Igor Š., Verica Đ., Draženka K., Gordan M., Viktor N. Efficiency Assessment of Natural Biopolymers as Encapsulants of Green Tea (Camellia sinensis L.) Bioactive Compounds by Spray Drying. Food Bioprocess Technol. 2015: 1-17. https://doi.org/10.1007/s11947-015-1592-y |
[4]
.
3.5. XRD
Generally, solubility of substances in amorphous state is higher than the one in crystalline state. Since solids in amorphous state have randomly arrangement of molecules and atoms compared to ordered arrangement in the case of a crystal, lower energy is required to dissociate them
[12] | Hellen K. S., Monika P. T., Alexandre L. P., Marcos A. S. S., Mauro C. M. L. Evaluation of cross-linked chitosan microparticles containing acyclovir obtained by spray-drying. Mater Sci Eng C. 2009; 29: 387–392. https://doi.org/10.1016/j.msec.2008.07.030 |
[12]
.
Figure 4 depicts the X-ray diffraction pattern of native starch, willow bark extract and encapsulated powder. As shown in
Figure 4, the native starch exhibited a strong reflection peak at around 16.65º and several weak peaks at around 14º, 23º and 26º, indicating the existence of crystal structure. However, these peaks disappeared after encapsulation and diffused, fluctuated halo shape was observed. The XRD patterns demonstrated that encapsulation by spray drying could decrease crystallinity of starch. Similar results were found in previous report
[19] | Ordoñez M, Herrera A. Morphologic and stability cassava starch matrices for encapsulating limonene by spray drying. Powder Technol. 2014; 253: 89–97. |
[19]
.
Figure 4. XRD of native starch, willow bark extract and encapsulated powder.
3.6. Thermogravimetric Analysis/Derivative Thermogravimetry (TGA/DrTGA)
The thermogravimetric properties of three samples-willow bark extract, starch and encapsulated powder were described in
Figure 5. The thermal degradation of starch and encapsulated powder showed three stages while free willow bark extract showed constant decrease profile with multiple steps. In TGA figure of starch and encapsulated powder, the first mass loss around 140-150°C could be attributed to the loss of volatile compounds, especially dehydration of samples. The second stage may correspond to degradation of the glycoside bonds of starch. The final stage may be due to thermal degradation of glucose ring of starch and the decomposition of residual carbon
[6] | Dang X. G., Yang M., Shan Z. H., Shahnaz Mansouri, Bee K May, Chen X. D., Chen H., Meng Wai Woo. On spray drying of oxidized corn starch cross-linked gelatin microcapsules for drug release, Mater Sci Eng C. 2016 (in press). https://doi.org/10.1016/j.msec.2016.12.047 |
[6]
. Notably, thermal degradation of encapsulated powder occurred earlier than that of starch, which implies particles loaded willow bark extract were more thermally instable than native starch. However, in comparison of free willow bark extract, degradation of encapsulated powder was initiated at a higher temperature, indicating that a thermal protection of willow bark extract could be achieved by encapsulation process under around 200°C. This result was similar to previous report
[11] | Graciele L. N., Brunna C. B. B., Stephanie S. P., Silvani V., Fábio S. M., Elane S. P., Renata D. M. C. A. Microencapsulation of freeze concentrated Ilex paraguariensis extract by spray drying. J Food Eng. 2015; 151: 60-68. https://doi.org/10.1016/j.jfoodeng.2014.10.031 |
[11]
.
Figure 5. Thermogravimetric properties of starch (A), willow bark extract (B) and encapsulated powder (C).
3.7. Hygroscopicity
The willow bark extract powders and encapsulated powders were stored in 75.7% relative humidity at 25°C. After 3 days in this condition, the willow bark extract powders absorbed water, causing hardening and darkening of the powders. It could be due to carbohydrates in willow bark extract. In contrast, encapsulated powder stayed low moisture content and original color. At this point, measured hygroscopicity of willow bark extract powder and encapsulated powder was 26.7±0.5 and 14.9±0.4 g/100 g, respectively. The lower hygroscopicity of encapsulated powders showed its good storage stability.
3.8. Storage Stability
The changes of total polyphenols in willow bark extract and encapsulated powder for the period of 50 days were shown in
Figure 6. Total amount of polyphenols in willow bark extract decreased as time went by whereas it was relatively stable in the case of encapsulated powder. From this result, it is possible to induce that starch could provide the protective effect on the phenolic compounds during the storage. These results were consistent with previous reports
[11] | Graciele L. N., Brunna C. B. B., Stephanie S. P., Silvani V., Fábio S. M., Elane S. P., Renata D. M. C. A. Microencapsulation of freeze concentrated Ilex paraguariensis extract by spray drying. J Food Eng. 2015; 151: 60-68. https://doi.org/10.1016/j.jfoodeng.2014.10.031 |
[11]
.
Figure 6. Storage stability of willow bark extract and encapsulated powder at 4°C for 50 days. Values represent the mean± standard deviation.